Eyelid openness detection devices are known wherein boundary points of an eyelid and an eyeball are detected based on points where an edge value is a maximum value or a minimum value on a first order edge image representing the magnitude of density changes in a grayscale image (Japanese Patent No. 3143819).
Eyelid detection devices are also known wherein boundary points of an eyelid and an eyeball are detected by taking locations having a large change in value as an eyelid feature amount, rather than the maximum of first order derivative values (edge values) (Japanese Patent No. 4309927).